A typical configuration of a tester is described in U.S. Pat. No. 6,906,546 and schematically shown in FIG. 1. A wafer 6 rests on a substrate support 5. Attached to the frame 1 of the tester is a replaceable test probe 7, which is matched to the integrated circuit to be tested and which contacts, with its resilient test contacts 8, the electrical contacts of the wafer (i.e., the so-called bond pads of the integrated circuits, to which the bonding wires will be connected later) and connects the electrical contacts to electronics for testing the integrated circuits. Substrate support 5 is disposed on a Z-theta stage 4, by substrate support 5 can be moved along the Z-direction toward test contacts 8 and to be rotated about this Z-direction. Z-theta stage 4 is disposed on two intersecting linear axes 2, 3, by which substrate support 5 can be moved in the X- and Y-directions.
Wafer 6 is aligned with test probe 7 by means of the two linear axes 2, 3 and the axis of rotation of Z-theta stage 4. The Z-theta stage then presses the wafer onto test contacts 8, and a test program is started.
The spring force of an individual test contact 8 is small. However, since a large number of such test contacts come into action simultaneously, the force with which wafer 6 must be pressed against test probe 7 may be in the range of several thousands of newtons. In a tester according to FIG. 1, this large force between test probe 7 and wafer 6 must be transmitted to substrate support 5 via frame 1, linear axes 2, 3 and Z-theta stage 4, as is indicated by force loop 9. Therefore, all of these elements must be designed to withstand such forces. The individual components must be of correspondingly large and heavy construction.
In order to enable movement in the X- and Y-directions, it is also possible to use devices other than that illustrated in FIG. 1. Suitable devices include, for example, gantry arrangements as well as intersecting linear axes, such as described in U.S. Pat. No. 5,760,564, or planar motors, such as illustrated in U.S. Pat. No. 6,531,793. What is important is that the substrate support is movable relative to the test probe in two linearly independent directions parallel to a plane of the substrate support.
It has been proposed already in U.S. Pat. No. 7,656,174 to use a vacuum or a magnetic element (electromagnet) to generate the force between the test probe and the wafer. In this way, the force for pressing the test contacts onto the electrical contacts acts directly between the substrate support and the test probe. The frame of the tester and the other components are not loaded by these large forces and may be made lighter and smaller.
According to Moore's Law, future generations of integrated circuits will become increasingly more integrated and be made with finer structures and, therefore, will require increasingly complex tests. Reliable contacting of increasing numbers of increasingly smaller electrical contacts using increasingly finer test contacts requires increasingly precise process control, not only during manufacture of the integrated circuits, but also during testing.